mm43:
As takata has rightly pointed out, IAS greater than 60KTS AND/OR AoA less than 30 degrees are required to prevent the Abnormal Law activating. It is while in this AND/OR regime that a very clear warning needs to be given that the aircraft is stalled. IAS is useful, and AoA is useful, and it would be preferable to know each rather than being left in the dark because one or the other, or both wasn't deemed valid.
Any system that pressents "conclusions" to a user without access to the underlying raw data is inherently problematic, especially if there are unknown interactions. (Unknown or untrained for by the users).
Even if the raw data is suspect it should still be presented with a warning.
One analogy for the stall warning action would be an "idiot light" in a car without an oil pressure gauge that signals low oil but goes out if you overspeed the engine.
BTW: For a good example of bad outcome caused by sending "data invalied" rather than "possible error but here is best guess" see the
report for the destruction of the maiden flight of the Arieane5 launcher.